Synthesis of solid solutions Ln-Fe-O using aerosol spray pyrolysis method
Anastasia E. Goldt1,2, Albert G. Nasibulin1,3
1
Laboratory of Nanomaterials, Skolkovo Institute of Science and Technology, Moscow, 143026, Russia
2
Department of Materials Science Lomonosov Moscow State University, Moscow, 119991, Russia
3
Department of Applied Physics, Aalto University, Finland
Keywords: spray pyrolysis, perovskite, LnMnO3
Presenting author email: [email protected]
Rare-earth orthoferrites with the composition of LnFeO3
(Ln-rare earth element) demonstrate unique physical and
chemical properties for various applications, for
instance, gas separators, sensor and magneto-optic
materials, etc. LnFeO3 (Ln = La, Gd, Pr) have distorted
orthorhombic perovskite structure, where FeO6 as a
rotary tilted polyhedron fills the empty space left around
the Ln group. There is a mixed valence state of Fe2+/Fe3+
originated from the 3d iron ions in LnFeO3 resulted from
an anion deficiency, making LnFeO3 material with
prominent electrical and magnetic properties.
time down to 3 seconds. The number concertation of
particles depending on the conditions was varied and
controlled with a water based a TSI SMPS system.
SEM image of nanocrystalline particles (La-Fe-O)
prepared by ASP method is presented in Figure. Particles
are microspheres from 150 to 400 nm in the diameter.
Perovskites could be synthesized by simply heating the
corresponding metal oxides in a stoichiometric ratio. The
main difficulty in obtaining single-phase LnFeO3 is the
presence of undesired phases of Ln3Fe5O12 and Fe3O4.
Moreover, the garnet phase (Ln3Fe5O12) is
thermodynamically more stable than LnFeO3.
One important problem of the perovskite phase synthesis
is related to high processing temperature and therefore to
high energy consumption during the synthesis. For
increasing the chemical reaction rate and decreasing the
temperature of the synthesis, a various routes of softchemistry (for example glycine-nitrate combustion
reaction, sol-gel, co-precipitation method, hydrothermal
treatment, etc.) are usually used.
In the present work, we utilized an ultrasonic aerosol
spray pyrolysis method to prepare micron-sized
granules. This method is an effective technique to
prepare particles with a wide range of compositions of
controllable size from a few hundred nanometers to a
micrometer range. It is worth nothing that the method
allowed us to synthesize a product with homogeneous
composition, easy controllability, and short production
times.
The precursor solutions were prepared by dissolving a
stoichiometric amount of nitrate salts (La(NO3)3/
Fe(NO3)3; Gd(NO3)3/Fe(NO3)3; Pr(NO3)3/Fe(NO3)3) in
distilled water. The nitrate solutions were atomized using
an ultrasonic nebulizer with a resonant frequency of 1.7
MHz.
The aerosol flow was introduced into the quartz reactor
at 650 - 850 oC by nitrogen flow. The obtained particles
were collected downstream of the furnace on a filter. The
flow rate of nitrogen used as a carrier gas was varied
from 1 to 5 l/min, which corresponded to the residence
Figure. Particles produced at 700 oC
Phase transitions in the system Ln-Fe-O (Ln-La, Pr, Gd)
were analyzed in a wide temperature range (400-600 oC)
to obtain single-phase samples.
It was shown that our approach allowed us to obtain
single-phase LnFeO3 with a submicron grain size and
spherical micromorphology. The applications of the
particles for various markers have been tested.
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